1. Field of the Invention
The present invention relates to a convergence measuring apparatus and a method thereof, and more particularly, to a convergence measuring apparatus and a method thereof capable of precisely measuring the convergence while compensating the change of convergence caused due to the change of position and posture of a monitor, through an examining pattern of a predetermined shape formed of a color mixture of red, green, and blue.
2. Description of the Related Art
Generally, for a monitor or a television made of a color cathode ray tube (hereinafter called CRT), various suggestions for examining or adjusting the convergence have been made to prevent color deviation from an image.
FIG. 1 shows one of those suggestions in which photo sensors 5 or cameras (not shown) are adjacently disposed corresponding to a plurality of examining locations on a CRT screen 3 to measure the convergence. According to this suggestion, respective stripes of red, green, and blue (hereinafter called R.G.B. pattern) are shifted forward and backward, or leftward and rightward with respect to the examining locations to measure the light intensity detected by the photo sensors 5. Here, the convergence is measured based on the position of the R.G.B. pattern with respect to the light intensity detected by the photo sensors 5.
While the above suggestion has an advantage in that the convergence can be rapidly measured, it also has a disadvantage of requiring a relatively larger video space in order to secure sufficient movement range of the respective R.G.B. pattern. Accordingly, an offset by an overscan is always included in the measured convergence value, causing an error and incorrect measurement. Further, when an examined object or examining locations change, the positions of the photo sensors 5 also have to be changed in accordance with the respective examining locations, and flexibility deteriorates.
Another suggestion is shown in FIG. 2 in which the positions of the CRT 3 are adjusted appropriately while the convergence is measured by a single camera and a white pattern. According to this suggestion, the position of the CRT 3 is estimated by: obtaining a single image through a measuring camera 7 and a reference pattern of the CRT 3, and comparing the difference between the single image and the reference pattern. More specifically, a boundary line between an injection material covering the CRT 3 and the CRT 3 is detected for being compared with the boundary line of a reference image according to the position and posture of a predetermined image. As a result, the difference between the boundary lines is obtained, and the position and posture of the CRT 3 are estimated based thereon.
By the above suggestion, however, the estimation as to the position and posture of the CRT 3 largely depend on the examined object. Accordingly, when there is little change in the position and posture of the examined object, the image difference obtained through the single camera 7 is also decreased, and accordingly, it is difficult to measure the difference.
Further, according to the above-mentioned suggestion, the convergence is measured in a way that rhombuses of whitish color, i.e., the R.G.B. mixture, appear on the respective examining locations of the CRT 3, and are photographed by the detecting camera 7, i.e., color camera. Accordingly, due to the effect of the R.G.B. mixture, it becomes difficult to precisely measure the convergence. Further, the size of the rhombuses hinders exact formation of the rhombic pattern on the extreme ends of the video area of the monitor, and accordingly, it is difficult to precisely measure the locally varying convergence through the rhombuses.
Another suggestion to measure the convergence includes the processes of: detecting the convergence in a cross-hatch method by a single camera, while simultaneously obtaining a stereo image by an additional color camera: and estimating the CRT position and posture for compensation thereof. Here, the convergence is measured in a manner that the cross-hatch pattern of a whitish color, which is the mixture of R.G.B., appears on the CRT 3, and the image is photographed by the color camera for analysis thereof. Then, the changes of the CRT position and posture are measured through the stereo image of the CRT 3. This suggestion has an advantage in that a relatively precise measurement can be achieved since the changes of the CRT position and posture can be obtained by a considerably large value. Further, since there is no need for a reference examined object, this suggestion also has the advantage of high flexibility.
The above suggestion, however, still has a disadvantage in that the exact measurement is hindered by the effect of the color mixture, since the same uses the white color which is the R.G.B. mixture. Further, since the convergence is measured from locations spaced from the intersections of the cross-hatch pattern at predetermined distances, errors occur according to the respective locations. It is also quite difficult to measure the dynamic convergence at the respective corner areas of the CRT 3.
Accordingly, a new suggestion of measuring the convergence capable of preventing the effect of the color mixture has been suggested. This suggestion includes a monochrome detecting camera, and a pair of monochrome cameras arranged beside the monochrome detecting camera in a symmetrical manner. This suggestion includes the processes of: obtaining a stereo image by additionally provided pair of monochrome cameras while photographing a circular pattern which consists of the respective colors of R.G.B.; and estimating the change of position and posture of the monitor for compensation thereof. Since the convergence is measured in a manner that the monochrome cameras photograph the circular pattern consisting of the respective colors of R.G.B. for analysis and compensation, there is little effect of color mixture. Accordingly, a precise measurement can be achieved.
The above suggestion, however, has a disadvantage of having an incorrect arrangement of the pattern at the respective corners, which is caused due to a deteriorated spatial resolution when the circular patterns consisting of the respective colors of R.G.B. are produced on the CRT 3. Accordingly, the dynamic convergence is harder to measure. Further, since the pattern consisting of the respective colors of R.G.B. is produced by using electric guns for the respective colors of R.G.B., the characteristics of the CRT are not considered. Meanwhile, in order to adjust the CRT position and posture, there are two cameras used, causing another process for precisely calculating the characteristics of the respective cameras for application.
Various suggestions are described as above for measuring the convergence, which have advantages and disadvantages, respectively. As described, it is true that those suggestions hardly measure the dynamic convergence precisely while utilizing the patterns of color mixture based on the optical characteristics of the CRT. Accordingly, studies are in the progress to overcome the shortcomings of the above suggestions, and also to measure the convergence more precisely by compensating the effect by the convergence caused due to the CRT position and posture change, and by increasing the available difference of the CRT position and posture as possible.